Conventionally, an ultrasonic flaw inspection method is known as a method of nondestructively inspecting a structural member of an aircraft or the like. As a specific example, a damage length measurement system which can measure a length of damage, such as delamination or peeling, in an adhesive part or a bonded part, using an actuator which emits ultrasonic waves toward a region to be inspected and an FBG (fiber Bragg grating) sensor for receiving ultrasonic reflected waves reflected in the region to be inspected has been proposed (for example, refer to Japanese Patent Application Publication JP 2011-185921 A and Japanese Patent Application Publication JP 2014-194379 A).
Although a length and a size of damage in a range to be inspected can be measured by the conventional ultrasonic test method, only a local range, such as a bonded part, can be inspected. That is, only damage in a short distance from an actuator and a sensor can be detected. Specifically, an actuator and a sensor require to be disposed with an interval of not more than 300 mm at most. Therefore, an inspection of a large aircraft part or the like requires to dispose a large number of actuators and sensors with a high density, and that is not realistic.
Accordingly, an object of the present invention is to enable to nondestructively detect a damage in an object to be tested with targeting a wider range.